Human skin is exposed to visible light (V
L; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm
−2): one comprising V
L with less than 0.5% UVA1 (V
L+UVA1) and the other pure V
L. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm
−2 of V
L+UVA1 and pure V
L 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at V
L+UVA1 sites compared with pure V
L. Histology findings demonstrated a statistically significant increase in the marker of inflammation (
P < 0.05) and proliferation (
P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of V
L+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to V
L+UVA1 dose (~400 J cm
−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range.
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